I received some information that the next Olympus PEN camera will have a new design and will look more like the old PEN F film camera. In addition, the new camera is rumored to have a viewfinder (not sure if it will be optical or electronic). I have no other details for now.
Olympus announced the E-PL2 in January 2011, the E-P3 in June 2011 and the E-PL5 in September 2012 (Photokina). It is reasonable to expect the next PEN announcement will probably be this summer.